1. Field of the Invention
This invention relates to a method of targeting and imaging tumors in humans, by the use of micellar particles such as phospholipid vesicles. More particularly, the invention relates to a method of introducing neutral or charged phospholipid micellar particles containing a radiolabeled marker into a patient to diagnose such tumors.
2. Description of Prior Art
Before various abnormalities in a patient's body can be diagnosed and treated, it is often necessary to locate the abnormalities. This is particularly true of abnormalities such as malignant tumors since the treatment is often on a localized basis. Thus, the location of the malignant tumor must be identified so that therapy can be directed to such cancer cells for treatment.
Various attempts have been made over an extended number of years to identify specific locations, such as tumors, by simple techniques. For example, it would be desirable to identify the location of cancer cells by a simple method involving the localization of a particular chemical at the specific site. It would also be desirable to treat the cancer by introducing modified chemicals into the patient's body and having such chemicals move to specific locations to combat the cancer cells at such locations. In spite of such attempts, however, simple delivery systems for targeting tumors in humans do not exist as yet.
Placing a chemotherapeutic drug in the body orally, subcutaneously or intravenously can result in harm to the normal cells in the body which take up the drug and a worsening in the patient's condition, without achieving the desired reduction in tumor cell activity. In the past, this toxicity to normal cells in the patient's body has been a major disadvantage in the treatment of tumors with chemotherapeutic agents. The lack of efficacy of such chemotherapy is also attributable to the failure of the freely circulating drug to localize within tumor cells before it is excreted or taken up by other cells in the body.
Prior attempts to improve treatment of tumors by chemotherapeutic agents have included encapsulation of such agents within biodegradable phospholipid micellar particles in the form of vesicles or liposomes. Encapsulation is thought to reduce potential toxicity from the circulating drugs. Researchers have also sought to utilize such encapsulation to selectively target tumors within a body for delivery of chemotherapeutics. However, until the invention disclosed in application Ser. No. 663,503, filed Oct. 22, 1984, "Method of Targeting a Specific Location in a Body," now abandoned, and its parent application Ser. No. 363,593, filed Mar. 30, 1982, now abandoned, efforts to locate or treat tumor cells with drug-encapsulating targeting particles have not been successful.
The inability to provide a satisfactory particle targeting method is believed to be due to the nature of the solid tumors and their metastases which are located in extravascular tissues. Thus, to accomplish targeting of intravenously injected radiolabelled or chemotherapeutic particles to the tumor cells, the particles must leave the normal circulation by crossing the blood vessel membranes to enter the extravascular tissues. This movement is known as "extravasation". In addition the encapsulated agent must cross the tumor cell membrane. Normally, small substances such as small molecular weight proteins and membrane-soluble molecules can cross cell membranes by a process known as passive diffusion. However, passive diffusion will not allow sufficient accumulation of larger particles carrying drugs within cells to reach therapeutic levels. Additionally, cells can actively transport materials across the membrane by a process such as pinocytosis wherein extracellular particles are engulfed by the membrane and released inside the cell. Entry of encapsulating particles into individual cells may occur by pinocytosis.
Progress in targeting tumors with chemotherapeutic drugs has been hampered by the inability to accomplish and detect movement of drug carriers across blood vessel membranes. In the usual case, large structures such as drug encapsulating vesicles cannot escape from blood vessels such as capillaries, and thus remain in circulation.
An understanding of extravasation, however, requires an examination of the structure of the vascular morphology of a tumor. Various blood vessels are associated with tumors, in particular capillaries. It is now known that tumor capillaries may exhibit alterations in their structure, such as fenestrations, as a result of tumor cell growth patterns. H.I. Peterson, Vascular and Extravascular Spaces in Tumors: Tumor Vascular Permeability, Chapter III, Tumor Blood Circulation, H.I. Peterson, Ed. (1979). Studies of tumor capillary permeability reveal morphologic variations in the capillaries which allow some substances to cross the capillary membrane Such variations include defects in vascular endothelium from poor cell differentiation, or breaks in vascular walls as a result of invading tumor cells. H.I. Peterson, supra. Notwithstanding such knowledge of tumor vascular morphology, researchers such as Peterson have concluded that transport of large molecules or materials across the tumor capillary wall occurs as a result of passive diffusion and that "concentrations of active drugs sufficient for therapeutic effect are difficult to reach". H.I. Peterson, supra, at 83.
Prior to such morphologic studies, early reports suggested that vesicles might undergo transcapillary passage across the capillary membranes into tumor cells. G. Gregoriadis, Liposomes in Biological Systems, Gregoriadis, Ed., Ch 2, (1980). However, available data indicated that the vesicles were unstable in vivo and that the radiolabel may have leaked, thus apparently prompting the two alternative theories of (1) longer circulation of vesicles in the blood with release of drugs at a slower rate or (2) interaction of the liposomes with the capillary walls without crossing the wall surface, which would result in the appearance of drugs at the tumor sites, but without drugs within tumor cells. Id. Other researchers simply concluded that the vesicles do not penetrate vascular walls after intravenous administration. B. Ryman et al., Biol. Cell, Vol. 47, pp. 71-80 (1983); G. Poste, Biol. Cell, Vol. 47, pp. 19-38 (1983).
Thus, although the prior art has recognized that vesicles carrying radiolabel markers or therapeutic drugs must cross vascular barriers to reach tumor cells, the experience of the art has taught that intravenous administration is not effective to deliver the vesicles to extravascular tumor cells. In the aforesaid application, Ser. No. 663,503, and parent application, Ser. No. 363,593, "Method of Targeting a Specific Location in a Body", the disclosures of which are incorporated herein by reference, a method is provided for targeting tumors in vitro and in animals, specifically, mice. In the present invention, a method is provided for enhancing extravasation of radiolabelled particles to tumor cells within humans, for the identification of such tumor sites.